Magnetostriction teaching device



Nov. 9, 1965 J. SINGERMAN 3,216,131

MAGNETOSTRICTION TEACHING DEVICE Filed Jan. 23, 1962 lmllmrlm Q g mlmllm j 76 b8 7 Jose o mgerman IN V EN TOR.

United States Patent tic 3,216,131 Patented Nov. 9, 1965 3,216,131 MAGNETOSTRICTION TEACHING DEVECE Joseph Singerman, New York, N.Y. (11045 71st Road, Forest Hills 75, N.Y.) Filed Jan. 23, 1962, Ser. No. 168,172 1 Claim. (Cl. 35-19) This invention provides the instructor with a simple device which presents the student with striking evidence of dimensional change in ferromagnetic materials when a magnetic field is introduced. Use is made of a differentially magnetostrictive strip, hereinafter referred, to also, as the strip or bimetal strip. The strip consists of two different magnetostrictive materials, that is, two materials ditfering from each other in kind or magnitude of magnetostrictive response, bonded to form a strip resembling the wellknown thermostatic bimetal. It is mounted as a cantilever, within the open core of a solenoid of insulated wire. Change in length of one, or differential length change of the two materials, when a magnetic field is introduced by passing an electric current thru the solenoid, is, in effect, magnified into an appreciable deflection of the free end of the strip.

It is one object of this invention to provide a novel, striking and easily seen evidence of magnetostriction.

It is another aim of this invention to provide the teacher with a simple, rugged and convenient device, not requiring the use of delicate or expensive equipment nor of auxiliary equipment other than a standard current source.

A further object of this invention is to demonstrate the fact that materials differ in their magnetostrictive properties.

Another aim of this invention is to provide simple means for zero adjustment.

Still another aim of this invention is to provide damping of the natural vibration of the bimetal strip.

Further aims will be evident from a study of the disclosure, including the drawings, submitted herewith.

In the prior art, magnetostrictive change in length is magnified for observation, sometimes, by a lever or a series of levers. Differentially dimensional change of two different metals is demonstrated, indirectly, by the vibratory response of magnetostrictive transducers wellknown to the art. Other methods of demonstrating dimensional change of this order of magnitude, such as use of the interferometer, utilize optical reflection. All of these methods require the setting up and use of complex and delicate precision equipment. Such requirement makes it extremely diflicult, if not actually discouraging to attempt to demonstrate magnetostrictive dimensional change before a class.

A form of the apparatus is shown in partial section in FIGURE 1.

FIGURES 2, 3, 4 and 5 show mechanisms for zero adjustment different from that depicted in FIGURE 1.

FIGURE 6 is a fragmentary view showing damping vanes.

Referring more particularly to FIGURE, 1, the bimetal strip 1 consists of two differentially magnetostrictive elements, 2 and 3, bonded or welded together. In a preferred form of this invention, 2 is a strip of a metal chosen because of its marked positive magnetostrictive property, while the material of element 3 exhibits negative magnetostriction. Thus, when subjected to a magnetic field, element 2 tends to elongate while the element 3 tends to shorten.

The bimetal strip 1, anchored at one extremity, is free to bend transversely within the tube 4. This it does due to the differential elongation described above. The initial setting of strip 1 and its inherent elasticity are such as to cause it to bear against the end of adjustment screw 5. Turning this screw, one way or the other, will cause the strip to flex along that portion of its length extending from the point of contact with the screw to the anchorage 6. Thus, the index mark 7, at the free end of the strip, may be given an initial seting, before each demonstration, to register with a zero mark on the reference scale 8.

When an electric current is caused to flow thru solenoid 9, a magnetic field permeates the bimetal strip. The strain set up by the differentially magnetostrictive property of its elements 2 and 3, as explained hereinbefore, causes it to bend so that index mark 7 moves relative to the scale 8. It is essential, for the purpose of classroom demonstration, that the bimetal strip be deflected an appreciable distance to accomplish this, it is made narrow and long and is composed of very thin elements. A strip which I have used successfully is composed of elements measuring about 0.25 by 10 inches and having a thickness of about .005 inch.

An annoyance inherent in a thin, long bimetal strip, as described above, results from the almost certain fact that the materials chosen for this purpose, to constitute the two elements of the bimetal, will differ in thermal coefficient of expansion. Consequently, the bimetal strip will flex, more or less, in one direction or the other with fluctuation in ambient temperature. This makes it extremely desirable to incorporate in the apparatus a simple means for preadjusting the Zero setting before proceeding with each demonstration. Alternative mechanisms for the adjustment will be described hereinafter.

To avoid undue temperature change in the bimetal strip, while operating the apparatus, it is desirable to provide for dissipation of heat, resulting from resistance losses in the solenoid, conducted to the air surrounding the strip. Such provision is facilitated by the vents 10, 10 in the anchorage 6, permitting convection of air thru the tube 4.

An alternative means of providing for a zero adjustment is depicted in FIGURE 2. Here the scale plate 11 is free to be slid, transversely, along tracks 12, 12.

Other means of achieving zero adjustment would be accomplished by providing a device that would permit limited rotation, or tilting, of the entire apparatus, or of the coil and bimetal assembly, about an axis perpendicular to the drawing in FIGURE 1. In this way, the elasticity of the bimetal strip 1 will permit its weight, together with that of the platen 13, to cause the strip to flex, to the left or to the right, in accord with the direction and amount of tilt.

Such limited rotation, or tilt, may be provided for by any of several devices, such as those depicted in FIG- URES 3, 4, and 5.

FIGURE 3 shows a rod 14 integral with flange 15 which is attached to the back plate 16. The axis of this rod, thus, is perpendicular to the view shown in FIGURE 1. In use, the rod is set in a standard laboratory support rod clamp. To adjust the zero setting, the whole assembly is rotated a few degrees in the desired direction, and fixed at the position by tightening the clamp screw.

Another means for accomplishing rotation of the assembly is provided by the tilting screw 17, set in and near the left or right hand edge of the base 18, as shown in FIGURE 4. As the tilting screw is screwed downward, its lower extremity bears against the table top causing that edge of the base to rise, thereby bringing about an angular rotation of the apparatus, pivoted at the point of contact with the table of the opposite edge of the base.

The same rotational effect may be realized by inserting, between the table top and either the left or the right hand edge of the base 18, a wedge 19 as shown in FIG- URE 5. Pushing the wedge inward tilts the apparatus in the same manner as by use of the tilting screw 17 in FIGURE 4.

To improve visibility from more remote parts of a classroom, the index mark 7 is placed upon the more easily visible area of platen 13, afiixed to the free end of strip 1.

A slight disturbance will cause the bimetal strip to oscillate as a pendulum. To damp this oscillation, the material of the platen is bent back, at a right angle, at the two ends 20, 20, to form two damping vanes 22, 22 in FIGURE 6. Friction between the faces of these vanes and the air damps the unwanted oscillation.

Various obvious modifications of the forms of the invention herein described and illustrated may be made without deviating from my invention.

For example, the anchorage 6, in which the fixed end of the bimetal is attached, may be rotatably mounted, by means well known to the art, to provide for zero adjustment. And further,

The rod 14 of FIGURE 3 may pivot in any support in place of a laboratory support rod. And further,

Means other than current in a solenoid, such as a permanent magnet, may be used for introducing a magnetic field. And further,

Differential magnetostriction in the bimetal strip may be attained by combining two elements differing from each other in one of several respects, to wit: amount of dimensional change, sign of dimensional change or magnetic vs. non-magnetic property. And further,

A tilting screw may be incorporated near both the left and the right hand edges of the base. And further,

Instead of providing a rod 14 to be held in a support rod clamp, the apparatus may be held in a standard laboratory clamp which permits rotational adjustment. And further,

One damping vane, instead of two, may be incorporated. Whether this vane forms a part of the platen or is attached directly to the bimetal strip, it is obviously integral with the strip. And further,

Convection of air thru the tube 4 can be promoted by providing any kind of vent, other than the vents 10, 10, at or near the anchorage. For example, a vent may be provided extending thru the pedestal 21 and the lower extremity of the tube 4. And further,

The bimetal strip or the tube may be extended, in the opposite direction, beyond the anchored end, and they may there be provided with cooling fins to present additional area for dissipation of heat to the surrounding air. And further,

The said extension may be flared out or affixed to fins for added heat dissipation. And further,

The scale plate 11 may have but one reference mark, or it may slide in or upon one track instead of two; or it may be held by a pin passing thru a transverse slot, said slot serving as a track to permit transverse adjustment. And further,

The solenoid may be located at or below the fixed end of the bimetal, that is, on the side of the anchorage opposite that on which the scale is located. And further,

The reference mark may comprise either an inscribed line or any part of the structure that does not move with the free portion of the bimetal strip, just as the index mark 7 may simply comprise the end of the strip itself.

I claim:

A magnetostriction teaching device comprising a dilferentially magnetostrictive bimetallic strip, a support, said strip fixed at one end to said support, a solenoid on said support having an open core, said strip extending longitudinally thru the open core of said solenoid, a reference mark on said support in proximity to the free end of said strip, a platen and a damping vane integral with the free end of said strip, said platen having a mark adjacent to and cooperating with said mark on said support, and means for zero adjustment, said means provided by a screw so mounted that it bears against a face of the said strip at a point close to the said 'fixed end of said strip.

References Cited by the Examiner UNITED STATES PATENTS 269,796 12/82 Kirk et al 73-3635 X 305,499 9/84 Barton 73363.5 X 1,889,153 11/32 Pierce 32434 2,542,075 2/51 Firth 32434 2,780,774 2/57 Epstein 32434 2,850,697 9/58 Little 324 34 2,950,784 8/60 Hertel 73430 X FOREIGN PATENTS 13,539 1899 Great Britain.

OTHER REFERENCES Article, Magnetostriction Phenomena, appearing in General Electric Review, vol. 45, No. 3, March 1942, pages 161-163.

Cambosco Order Book for Science Supplies, 24th ed., 1954-1955.

JEROME SCHNALL, Primary Examiner. L. SMILOW, LAWRENCE CHARLES, Examiners. 

